Spatial Organization of Ran Signaling in plants
Iris Meier (MG/PCMB, The Ohio State University)
(February 19, 2004 11:30 AM - 12:30 PM)
Ran is a small GTPase with functions in nuclear transport, spindle formation, and nuclear envelope re-assembly. It exists in two forms, Ran-GTP and Ran-GDP, which are interconverted by the activity of two proteins. RanGAP turns RanGTP into RanGDP while RCC1 turns RanGDP into RanGTP. The spatial separation of RanGAP and RCC1 in the cell leads to the establishment of a gradient between Ran-GTP and Ran-GDP, which is important for the function of Ran. During interphase, RanGAP is cytoplasmic while RCC1 is located in the nucleus. This establishes a gradient of RanGTP to RanGDP across the nuclear envelope, which is involved in the directionality of transport between nucleus and cytoplasm. During animal mitosis, RCC1 remains bound to the chromosomes while RanGAP migrates to the spindle apparatus. The resulting mitotic gradient of Ran has been shown by imaging methods in live cells. We have found that like animal RanGAP, plant RanGAP is associated with the nuclear envelope during interphase. However, during mitosis, it appears at the newly forming cell plate, a structure unique to plants. A specific N-terminal domain of plant RanGAP is necessary and sufficient for targeting the protein to the plant nuclear envelope in interphase and to the cell plate in mitosis. We conclude that the spatial re-organization of the Ran gradient during mitosis differs in plants and animals. We are interested in measuring and possibly modeling the gradient in plant cells.